This invention relates to the identification and location of ground faults in normally ungrounded a-c or d-c power distribution systems.
Private power distribution systems are frequently ungrounded, that is, neither side of the distributed voltage is tied directly to ground. In some cases there may be an earth ground connection, but the connection may be made through a high resistance (a thousand ohms or more). The advantage of such an arrangement is that when a first ground fault occurs the fault current is either zero (in the case of no initial ground connection) or only a few milliamperes. If the first ground fault is detected and cleared before a second ground fault occurs in the other line a more serious or catastrophic fault can be prevented.
To detect the occurrence of the first fault in such systems, ground relays are typically employed. The first ground fault causes a voltage to be applied to the coil of the ground relay and the resultant operation of the relay sounds an alarm indicating the fault has occurred.
Unfortunately, the alarm gives no indication of the fault location within the distribution system. In the absence of a more sophisticated fault locator, the maintenance person must then proceed to isolate the fault by opening branch circuit breakers until the alarm is silenced, in this way determining on which branch circuit the fault is located. The disadvantage of this procedure is that several branch circuits must typically be powered down before the fault is located, with electrical service to unfaulted branches being unnecessarily interrupted.
What is needed is a convenient and effective means for locating the fault or identifying the branch circuit in which is has occurred without interrupting service to any part of the system. Once the fault has been located, only the faulted branch need be opened for repair.